The present invention relates to a low-consumption hot-cathode X-ray tube which can be used as a source of quasimonochromatic radiation, in particular for apparatus for spectrometry, diffractometry and microradiography.
In an article of a Dutch review "NUCLEAR INSTRUMENTS AND METHODS", Vol. 78, n.degree. 2, of Feb. 15, 1970, pages 305 to 313, there were described hot and cold-cathode X-ray tubes which have a combined target-window in the form of a plate located at the end of the tube, allowing the emission of virtually monochromatic X-ray radiation due to the fact that the anode at the same time forms a filter for the radiation which it produces, which filter enhances characteristic lines of the emitted spectrum.
The use of a cold cathode implies the stabilization of the anode current, which is a matter of some difficulty, by continuous pumped evacuation to provide a primary vacuum and by using a controllable bleed device controlled by the curreent to stabilize the residual gas pressure in the tube. The pumping unit and controllable bleed device used for this purpose have a weight and electrical energy consumption which are too high for them to be made easily transportable.
The present invention relates to an advantageous embodiment of a low energy consumption, hot-cathode X-ray tube having an end-mounted anode, which can be used in transportable X-ray apparatus such as soil spectrometers, which are intended in particular for analyzing relatively light elements (having an atomic number Z lower than 45) by means of X-ray fluorescence, by exciting their K spectra. Heavier elements may also be analyzing analysed by using their L spectra.
According to the invention, there is provided a hot-cathode X-ray tube having a metal anode in the form of a plate located at its end, perpendicularly to the axis of the electron beam, which beam bombards the anode in such a way that at least part of the useful beam of X-rays produced by this bombardment passes through the thickness of the anode, which filters the beam by allowing to pass the characteristic radiation of the material forming the anode, further comprising: a first additional electrode of annular shape provided with a central opening and which is arranged in the path of the electron beam near the anode and parallel thereto, the said first additional electrode being at the same potential as the anode and having at least its surface made of the same metal as the said anode, whereby the radiation therefrom is supplemented by radiation due to electrons back-scattered as a result of elastic collision with the anode and which strike the first additional electrode.
The invention will be better understood and others of its features and advantages will become apparent from the following description and from the single accompanying FIGURE relating thereto, given by way of example.